1. Field of the Invention
The present invention relates to a sheet processing apparatus that performs a sheet folding process and an image forming system including the same.
2. Description of the Related Art
Conventionally, sheet processing apparatuses, which perform various post processing on a sheet on which an image is formed, have been proposed as auxiliary apparatuses of image forming apparatuses. Here, the “post processing” refers to various kinds of processing such as sorting sheets into a given number of copies, binding sheets using staples, folding sheets in a half-fold form, a tri-fold form (a z-fold form), or in other forms, and punching holes for filing. Of these sheet processing apparatuses, as a sheet processing apparatus (a sheet folding apparatus) that performs a sheet folding process, there has been known an apparatus that bends a sheet by brining the sheet into contact with a stopper and causing folding rollers to nip the bended sheet to form a folding line in a sheet (that is, performs a folding process on a sheet). In the folding system that forms the folding line on the sheet in a manner of nipping the sheet with the folding rollers, it is very important and strongly requested by users that a direction of the folding line is parallel to the front edge of the sheet, that is, that the folding line does not deviate to be oblique to the front edge of the sheet. In the following description, a state in which the folding line deviates to be oblique to the edge of the front edge of the sheet is referred to as “oblique deviation” of the folding line. For example, it is likely that the oblique folding line of the sheet is generated when the size of a sheet as a processing target changes or when a folding type or a folding mode of a sheet changes.
Japanese Patent No. 4238193 discloses a sheet folding apparatus capable of correcting oblique deviation of a sheet. The sheet folding apparatus includes a folding plate that is arranged to move forward or backward in a direction substantially perpendicular to a sheet conveying path, and an angle changing unit that changes a relative angle between an arbitrary edge of a sheet and a folding line and that is arranged on a tail edge fence on which a front edge of a sheet linearly conveyed along the conveying path abuts.
Further, Japanese Patent No. 4425101 discloses a sheet processing apparatus including a configuration that a pair of conveying rollers rotatable clockwise and counterclockwise is disposed downstream of a first folding roller in the sheet conveying direction; the pair of conveying rollers is stopped at a predetermined timing in order to nip a predetermined position of a sheet therebetween, and thereby to determine the sheet folding position. The apparatus further includes a configuration that an abut stopper is disposed upstream of a second folding roller; a front edge of the sheet is abut on the abut stopper so that a tail edge of the sheet is guided to the second folding roll, and thereby the sheet folding position can be determined.
In recent years, there have been market needs for compact and small products, including a need for slim product. In order to respond to the needs, it is required to reduce a space, in which a sheet folding process is performed, in a sheet processing apparatus.
However, in the conventional sheet processing apparatuses disclosed in Japanese Patent No. 4238193 and Japanese Patent No. 4425101, there is a problem in that it is difficult to correct the oblique deviation of the folding line of the sheet while reducing a space in an apparatus.
In addition, in the sheet processing apparatus that performs the sheet folding process, there is a case in which the position of the folding line relative to the front edge of the sheet is required to be changed. The oblique deviation of the folding line needs to be corrected even when the position of the folding line of the sheet is changed.